• Title/Summary/Keyword: Dimensionless Variable

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The Influence of Variable Thermophysical Properties for Filmwise Condensation of Superheated Vapor on a Vertical Wall (수직 벽에서 과열증기의 막응축에 대한 열물성의 영향)

  • 김경훈;성현찬
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.12 no.3
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    • pp.235-243
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    • 2000
  • A theoretical model for laminar filmwise condensation along an isothermal vertical wall at constant pressure has been formulated on the basis of conservation laws and other fundamental physical principles. The model was applied to the prediction of the influences of variable thermophysical properties of liquid and vapor layers in the filmwise condensation of superheated vapor of Rl2, R134a, R142b and R152a. The dimensionless velocity component method was employed in the transformation of the governing equations and their boundary conditions, and the polynomial method was used for treating variable thermophysical properties of liquid and vapor. Physical quantities, such as the dimensionless thickness of the liquid layer, local heat transfer rate and mean heat transfer coefficient, were investigated for different values of the superheated temperature of the stagnant vapor far from the wall. It was found that the value of mean heat transfer coefficient of R134a was higher than other refrigerants for the change of the superheated temperature.

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Vibration Analysis of Rotating Blades with the Cross Section Taper Considering the Pre-twist Angle and the Setting Angle (초기 비틀림각 및 장착 각의 영향을 고려한 단면 테이퍼진 회전 블레이드의 진동해석)

  • Lee, Jun-Hee;Yoo, Hong-Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.20 no.1
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    • pp.10-21
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    • 2010
  • Equations of chordwise and flapwise bending motions for the vibration analysis of rotating pre-twisted blades having tapered cross section and setting angle are derived by using hybrid deformation variable modeling. The two motions are couples to each other due to the pre-twisted angle of the beam cross section. The derived equations are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters on the modal characteristics of rotating pre-twisted blades having tapered cross section and orientation angle are investigated. The eigenvalue loci veering phenomena are also investigated and discussed in this work.

Vibration analysis of rotating blades considering the cross section taper, the pre-twist angle, and the setting angle (단면 테이퍼, 초기 비틀림각, 그리고 장착 각의 영향을 고려한 회전 블레이드의 진동해석)

  • Lee, Jun-Hee;Yoo, Hong-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.04a
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    • pp.288-295
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    • 2009
  • Equations of chordwise and flapwise bending motions for the vibration analysis of rotating pre-twisted blades having tapered cross section and orientation angle are derived by using hybrid deformation variable modeling. The two motions are couples to each other due to the pre-twisted angle of the beam cross section. The derived equations are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters on the modal characteristics of rotating pre-twisted blades having tapered cross section and orientation angle are investigated. The eigenvalue loci veering phenomena is also investigated and discussed in this work.

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Vibration Analysis of a Rotating Blade Considering Pre-twist Angle, Cross Section Taper and a Concentrated Mass (초기 비틀림 각과 단면 테이퍼 그리고 집중질량을 갖는 회전하는 블레이드의 진동해석)

  • Kim, Hyung Yung;Yoo, Hong Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.4
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    • pp.338-346
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    • 2013
  • Equations of motion of a rotating blade considering pre-twist angle, cross section taper and a concentrated mass are derived using the hybrid deformation variable modeling method. For the modeling of a concentrated mass which is located at an arbitrary position of the blade, a Dirac delta function is employed for the mass density function. The final equations for the vibration analysis are transformed into a dimensionless form using several dimensionless parameters. The effects of the dimensionless parameters on the vibration characteristics of the rotating blade are investigated through numerical analysis.

Effect of Fluid Viscosity on the Suspension of a Single Particle in Channel Flow (채널 유동에서 점성이 단일 입자 혼합 유동의 suspension에 미치는 영향)

  • Choi, Hyoung-Gwon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.3
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    • pp.194-200
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    • 2009
  • Suspension of a single solid particle in a channel flow with a constant pressure gradient is studied numerically. The interaction of a circular particle with a surrounding Newtonian fluid is formulated using a combined formulation. Numerical results are presented using two dimensionless variables: the sedimentation Reynolds number and the generalized Froude number. From the present results, it has been shown that a solid particle is suspended at a smaller generalized Froude number as the viscosity of the surrounding fluid increases. The time taken for equilibrium position is found to be smaller as fluid viscosity increases when both : the sedimentation Reynolds number and the generalized Froude number are the same while, at the same situation, the dimensionless time taken for equilibrium position is to be nearly the same regardless of fluid viscosity when a dimensionless time variable is introduced

STEADY NONLINEAR HYDROMAGNETIC FLOW OVER A STRETCHING SHEET WITH VARIABLE THICKNESS AND VARIABLE SURFACE TEMPERATURE

  • Anjali Devi, S.P.;Prakash, M.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.18 no.3
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    • pp.245-256
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    • 2014
  • This work is focused on the boundary layer and heat transfer characteristics of hydromagnetic flow over a stretching sheet with variable thickness. Steady, two dimensional, nonlinear, laminar flow of an incompressible, viscous and electrically conducting fluid over a stretching sheet with variable thickness and power law velocity in the presence of variable magnetic field and variable temperature is considered. Governing equations of the problem are converted into ordinary differential equations utilizing similarity transformations. The resulting non-linear differential equations are solved numerically by utilizing Nachtsheim-Swigert shooting iterative scheme for satisfaction of asymptotic boundary conditions along with fourth order Runge-Kutta integration method. Numerical computations are carried out for various values of the physical parameters and the effects over the velocity and temperature are analyzed. Numerical values of dimensionless skin friction coefficient and non-dimensional rate of heat transfer are also obtained.

Stress Intensity Factors of Combined Mode(Mode I/II) Crack in a Variable Thickness Plate (두께가 변화하는 부재 내의 혼합모드(모드 I/II) 균열의 응력확대계수)

  • 조명래;양원호;최용식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.1875-1882
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    • 1993
  • Variable thickness plates are commonly used as structural members in the majority of industrial sectors. Previous fracture mechanics researches on variable thickness plates were limited to mode I loading cases. In practice, however, cracks are usually located inclined to the loading direction. In this respect, combined mode(mode I/II) stress intensity factors $K_{I}$ and $K_{II}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a slant edge crack were chosen. The parameters used in this study were dimensionless crack $length{\lambda}$, slant $angle{\alpha}$, thickness $ratio{\beta}$ and width ratio{\omega}$. Stress intensity factors were calculated by crack opening displacement(COD) and crack sliding displacement(CSD)method proposed by Ingraffea and Manu.

Stress Intensity Factors of a Combined Mode (I/III) Crack in a Variable Thickness Plate -CT Type- (두께가 변화하는 부재 내의 혼합모드 (I/III)균열의 응력확대계수 -CT형-)

  • 조명래
    • Journal of the Korean Society of Safety
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    • v.13 no.3
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    • pp.24-31
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    • 1998
  • Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode I/III stress intensity factors $K_I$ and $K_III$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. The parameters used in this study were dimensionless crack length $\lamda$, crack slant angle $\alpha$, thickness ratio $\beta$ and width ratio $\omega$. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method.

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A Comparative Study on Eigen-Wear Analysis and Numerical Analysis using Algorithm for Adaptive Meshing (마모해석을 위한 고유치해석과 Adaptive Meshing 알고리듬을 이용한 수치해석 비교)

  • Jang, Ilkwang;Jang, Yong Hoon
    • Tribology and Lubricants
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    • v.36 no.5
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    • pp.262-266
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    • 2020
  • Herein, we present a numerical investigation of wear analysis of sliding systems with a constant speed subjected to Archard's wear law. For this investigation, we compared two methods: eigen-wear analysis and adaptive meshing technique. The eigen-wear analysis is advantageous to predict the evolution of contact pressure due to wear using the initial contact pressure and contact stiffness. The adaptive meshing technique in finite element analysis is employed to obtain transient wear behavior, which needs significant computational resources. From the eigen-wear analysis, we can determine the appropriate element size required for finite element analysis and the time increment required for wear evolution by a dimensionless variable above a certain value. Since the prediction of wear depends on the maximum contact pressure, the finite element model should have a reasonable representation of the maximum contact pressure. The maximum contact pressure and wear amount according to this dimensionless variable shows that the number of fine meshes in the contact area contributes more to the accuracy of the wear analysis, and the time increment is less sensitive when the number of contact nodes is significantly larger. The results derived from a two-dimensional wear model can be applied to a three-dimensional wear model.

Numerical Experiments of the Behavior of Bars in the Channels with Periodic Variable Width (주기적인 하폭 변화 수로에서 사주의 거동에 관한 수치실험)

  • Jang, Chang-Lae
    • Journal of Korea Water Resources Association
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    • v.47 no.1
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    • pp.37-47
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    • 2014
  • This study examines the processes and the behaviour characteristics of forcing bars in channels with periodic variable width in the alternate and braided regimes by using a two dimensional numerical model. The wavelength and the migration speed decrease as the amplitude of variable width increases. The forcing effects of the width variation on the alternate bars is stronger than those on the braided bars. The bar migration speed increases as the dimensionless amplitude in the braided regime is 0.25. However, the migration speed is abruptly decreased as the amplitude in it was larger than 0.25. The bar migration speed increases in the alternates bar regime as the dimensionless wavelength increases. However, the migration speed decreases around 1 of the wavelength. As the bar wavelength and the variable width wavelength coincide, the bars don't migrate downstream by the strong forcing effects on the bars due to the suppression by the width variation.